One of the best things about owning a computer is being able to emulate your favorite console. Emulation allows your computer to think like a video game console.
There were three Ecco the Dolphin titles released for the Sega Genesis; Ecco the Dolphin, Ecco 2: The Tides of Time and Ecco Jr. The Japanese version of the original Ecco featured a new level called "The Stomach". There are also several prototypes of Ecco 2 floating around with the most prominent and earliest of them being the one featured on the downloads section of this article.
Ecco the Dolphin for Sega Genesis seemed to be the least complete of the original Ecco the Dolphins. Many of the story elements present in the Game Gear version were either difficult to find or not there.

For example in the Game Gear version it was mandatory you helped a Dolphin find her family to gain two special songs needed for Jellyfish and Sharks. In the Genesis version you could skip this plot element completly and finish the level.

Ecco 2: The Tides of Time has to be one of the best games for the Sega Genesis. Ecco must travel through two alternate futures to save his friend the Asterite. The Japanese version of the game has an alternate epilogue from the American and European releases. There is also a prototype version known as the playable preview that has a cybernetic shark/dolphin you have to fight in the dark Vortex future.

Ecco Jr. is an education title designed for small children that featured the choice of three playable characters. The game is all about puzzles so you don't have to worry about getting hurt by sharks or jellyfish.
Using an emulator we have provided all the ROMs on the download portion of this article. You will need an emulator to play them so be sure to check out the Sega Genesis Emulation article.
Download:Related: Sega Genesis Emulation